1. Field of Invention
The present invention relates to a fan and in particular to a blower.
2. Related Art
With the development of electronic devices, the demands for heat dissipation also increase. Therefore, the heat dissipation technology has become an important issue of the computer industry. Since fans have the advantages of low costs and mature development, fans are often used for heat dissipation.
As shown in FIG. 1, a conventional blower 1 includes an impeller 11 and a housing 12. The housing 12 has an accommodating portion 121 where the impeller 11 is disposed. Moreover, the housing 12 has an outlet h1 and a throat portion T1. The throat portion T1 is adjacent to the outlet h1. When the blower 1 operates, the airflow flows out from the outlet h1. The throat T1 is used to prevent the airflow from being brought back into the accommodating portion 121 by the impeller 11 and thus reducing the air flux.
Please refer FIGS. 1 to 2B. FIG. 2A shows the fast Fourier transform (FFT) frequency spectrum demonstrating prominence ratio of a conventional blower 1. FIG. 2B shows the FFT frequency spectrum demonstrating the noise volume of the conventional blower 1. As shown in FIG. 2B, the conventional blower 1 produces a frequency peak P2 in the frequency spectrum demonstrating the noise is ultra-high when the impeller rotates at a particular speed (frequency). The highest noise volume at the frequency peak P2 is about 25 decibel (dB). In FIG. 2A, there is a prominence ratio peak P1 corresponding to the frequency peak P2 in FIG. 2B. The prominence ratio peak P1 of the conventional blower is about 5.24 dB. Therefore, although the use of the throat portion T1 can prevent air from flowing back into the accommodating portion 121, the continuous impact of the air flux on the throat portion T1 produces a rapid change in pressure. This results in the problem of high noise peak value P2 and high prominence ratio peak value P1 in the conventional blower 1.